1. Field of the Invention
The present invention relates generally to devices for monitoring the level and temperature of a liquid flowing through a fluid handling system and, more particularly, to a monitoring apparatus for providing an alarm when the flow or temperature of a liquid within a refrigeration system falls outside an established acceptable range of values.
2. Discussion of the Prior Art
Refrigeration-cycle systems are used to provide cooling in everything from residential air conditioners to commercial freezers such as those employed to cool refrigerated or frozen food counters in grocery stores.
A conventional commercial refrigerator or freezer includes a condenser, an evaporator, liquid and suction lines connected between the condenser and the evaporator to form a closed coolant system, a compressor, and a thermostatic expansion valve in the liquid line adjacent the evaporator. A liquid control valve is typically provided in the liquid line and is movable between a closed, defrost-cycle position restricting the flow of liquid through the liquid line, and an open, refrigeration-cycle position.
It is a known practice to defrost a commercial refrigeration system daily, and frequently twice daily, in order to maintain the efficiency of the system and prevent the formation of ice within the counter. An electrical circuit is provided in conventional systems for controlling the defrost cycle, and includes a switch for permitting operation of the liquid control valve to switch the system between the defrost cycle and the refrigeration cycle.
In order to permit maintenance personnel to monitor the level of refrigerant in the system, it is known to provide a sight glass within the liquid line which enables the personnel to view the flow of liquid through the line. When bubbles are visible in the line, low levels of coolant are present, providing an indication that replenishment is required. However, a certain amount of coolant is typically lost from the system before bubbles ever begin to appear in the sight glass, rendering early detection of coolant lose impossible.
This shortcoming in conventional systems has become significant in recent years with the concern for protecting the ozone from depletion due to the release of freon and other coolants to the atmosphere. Within the last four years, largely due to government imposed taxes, the price of freon has increased by a factor of five, bringing to the forefront a need to conserve freon in refrigeration systems whenever possible, and to stop leaks at an early stage.
New refrigeration systems are being marketed which include complicated monitoring systems for monitoring the level of liquid refrigerant in a receiver tank of the system, and which are capable of detecting certain types of leaks in the system. However, these systems are very expensive, and do not address the need of providing a reliable monitoring apparatus capable of use in existing, older units.
As disclosed in U.S. Pat. No. 3,059,443, issued 23 Oct. 1962 to Garner, an alarm apparatus for a refrigeration system is provided for detecting low levels of refrigerant within the system. The apparatus includes a T coupling in communication with the fluid pressure line of the system, and a thermistor resistance element exposed within a gas bubble entrapment portion of the coupling. A circuit is also provided for sensing the current through the thermistor and activating an alarm when the current exceeds a value corresponding to a sensed temperature above a predetermined value.
While this conventional device provides an accurate detection of low liquid levels in a closed refrigeration system, the device will not operate when air is present in the system.
Specifically, air may be introduced into the system during initial setup thereof or during replacement of system components, and it is possible that some of this air will remain in the system even though efforts are made to remove such air by evacuating the system. This air is harmful to the system and may become trapped within the gas bubble entrapment portion of the conventional alarm device, forcing the coolant away from the thermistor and causing the alarm to sound. So long as the air remains in the system, the alarm will continue to sound in the conventional device even though sufficient refrigerant is present.